Command register 1 – National Instruments PC-LPM-16/PnP User Manual

Page 76

Appendix D Register-Level Programming

PC-LPM-16/PnP User Manual

D-4



National Instruments Corporation

Command Register 1

Command Register 1 indicates the input channel to be read and the interrupt enable bits.

Address:

Base address + 00 (hex)

Type:

Write-only

Word Size:

8-bit

Bit Map:

Bit

Name

Description

SCANEN*

Scan Enable Bit—This bit enables or disables
multichannel scanning during data acquisition. The
power-on value is 1. If this bit is cleared, analog
channels MA<3..0> through 0 are sampled
alternately. If this bit is set, a single analog channel
selected by MA<3..0> is sampled during the entire
data acquisition operation. In order to perform single-
channel sampling, the UP/DOWN bit in Command
Register 2 must be clear before setting SCANEN* to
1. To set up a scanning mode, two consecutive
writings of this register are necessary. First, write the
desired valve to the UP/DOWN bit in Command
Register 2 if the UP/DOWN bit is not currently set to
its proper value. Then write MA<3..0> with
SCANEN* set to load the scan counter. Then write
MA<3..0> with SCANEN* cleared to enable
scanning.

For example, if the UP/DOWN bit is 0 and MA<3..0>
is 0011 and SCANEN* is first set, then cleared, analog
input channels 3 through 0 are sampled alternately
during subsequent data conversions. If SCANEN* is
set and is not cleared (with MA<3..0> still set to
0011), only analog input channel 3 is sampled during
the subsequent data conversions.

See the

Programming Multiple A/D Conversions with

Channel Scanning

section later in this appendix for

more information.

SCANEN*

CNTINTEN

EXTINTEN

FIFOINTEN

MA3

MA2

MA1